color_term is false or the class
resolves to no attributes.
Unlike ansi_format/4 this does not write to a stream and thus does
not require a terminal. It is used to decorate strings that are
handed to code that is not aware of colors, notably the toplevel
prompt (see the Prolog flag toplevel_prompt). As the caller
controls where the sequence ends up, the caller is also responsible
for verifying that the destination is a terminal and for emitting
the reset sequence `\e[0m`.